Rheological additives are chemical compositions, which, added even in small amounts, modify a liquid system's rheological properties, such as viscosity and response to shear. Such additives or thickeners may be used in a variety of liquid systems including aqueous systems such as paints, aqueous inks, and personal care products and compositions for treating subterranean formations. The additives improve the rheological properties by also affecting the dispersion, suspension and emulsification of pigments, binders and other solids within a vehicle.
Hydrophobically modified alkali swellable emulsion (HASE, also known as Hydrophobically modified alkali soluble) polymer systems and alkali soluble emulsion (ASE) polymer systems are commonly employed to modify the rheological properties of aqueous emulsion systems. These polymers are substantially insoluble in water at a low pH. However, at higher pH they become swellable or soluble in water and thus exhibit thickening behavior. Under the influence of a base, organic or inorganic, the HASE particles gradually swell and expand to form a three-dimensional network by intermolecular hydrophobic aggregation between HASE copolymer chains and/or with components of the emulsion. This network, combined with the hydrodynamic exclusion volume created by the expanded HASE chains, produces a thickening effect. This network is sensitive to applied stress so it breaks down under shear and recovers when the stress is relieved. Such rheological properties are particularly desirable for paints and coatings because they make the formulation easy to apply onto a surface while providing the thickness needed for uniform coverage and avoid spattering.
These alkali-swellable and alkali-soluble polymers are carboxyl functional polymers synthesized by free radical polymerization. Generally, HASE copolymer systems can be prepared from the following monomers: (a) an ethylenically unsaturated carboxylic acid, (b) a nonionic ethylenically unsaturated monomer, and (c) an ethylenically unsaturated hydrophobic monomer.
Latex is an example of an emulsion polymer which is a water-based polymer dispersion. Latex paints are used for a variety of applications including interior and exterior, and flat, semi-gloss and gloss applications. Latex is a stable dispersion (colloidal emulsion) of rubber or plastic polymer microparticles in an aqueous medium. Latexes may be natural or synthetic.